Modern petroleum drilling and production operations demand a great quantity of information relating to the parameters and conditions downhole. Such information typically includes the location and orientation of the borehole and drilling assembly, earth formation properties, and drilling environment parameters downhole. The gathering of information relating to formation properties and conditions downhole is commonly referred to as “logging”, and can be performed during the drilling process or separately from the drilling process.
Various measurement tools exist for use in logging while drilling (LWD). One such tool is the electromagnetic resistivity tool, which includes one or more antennas for transmitting an electromagnetic signal into the formation and one or more antennas for receiving a formation response. When operated at low frequencies, the electromagnetic resistivity tool (resistivity tool) may be called an “induction” tool, and at high frequencies it may be called an electromagnetic wave propagation tool. Though the physical phenomena that dominate the measurement may vary with frequency, the operating principles for the tool are consistent. In some cases, the amplitude and/or the phase of the received signals are compared to the amplitude and/or phase of the transmitted signals to measure the formation resistivity. In other cases, the amplitude and/or phase of the different received signals are compared to each other to measure the formation resistivity.
One or more tilted antennas may be included in the resistivity tool and other various logging tools, and a tilted antenna may by physically tilted at a certain angle relative to the tool axis. However, because of electromagnetic interference, e.g. from the tool, a tilted magnetic dipole of the antenna is not necessarily equal to the physical tilt of the antenna as is desired. This discrepancy decreases the accuracy of the logging tool, which decreases efficiency and reliability of all processes and decisions based on the logging data.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.
Notation and Nomenclature
Certain terms are used throughout the following description and claims to refer to particular system components and configurations. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or a direct connection, e.g. mechanical or electrical connections. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. In addition, the term “attached” is intended to mean either an indirect or a direct physical connection. Thus, if a first device attaches to a second device, that connection may be through a direct physical connection, or through an indirect physical connection via other devices and connections.